This invention relates to rotary cutting tools, and, while not so limited, is particularly suited to use with milling cutters.
For illustrative purposes, this specification will describe the invention as it pertains to a conventional end mill, i.e., a milling cutter of cylindrical configuration having a shank portion and a cutting portion, the cutting portion containing a plurality of helically disposed teeth extending from the shank end of the cutting portion to the free end thereof. In such a milling cutter the cutting edges of the teeth lie on a substantially constant radius with respect to the longitudinal axis of the tool. However, the invention may also have application to taper end mills wherein the cutting portion is generally frusto-conical in form, and the cutting edge of each tooth has a constantly decreasing radius with respect to the longitudinal axis of the tool as the edge extends from the shank end of the cutting portion to the free end or print, although even in such tapered end mill, the cutting edges of the teeth are at the same radius from the longitudinal axis of the tool in any plane through the cutting portion and perpendicular to the longitudinal axis of the tool. The invention also has application to so-called "straight fluted" end mills wherein the teeth extend parallel to the longitudinal axis of the tool, as opposed to helically with respect thereto, and of course the invention may also be utilized with other forms of rotary cutting tools which are not properly categorized as end mills or milling cutters generally.
There are several problems inherent in the use of the conventional milling cutter as described above. Generally speaking, these problems manifest themselves in excessive wear and relatively poor cutting action, or both, owing to the fact that the entire length of a cutting edge may be applied to the work piece at the same time, and owing to the fact that continuous chips are produced which are not satisfactorily removed from the work area. There have been many attempts made to improve the cutting action and decrease the wear in such tools, and these attempts usually involve the use of so-called "chip breakers" in the form of relatively deep notches cut transversely into the teeth at spaced intervals, or some other similar means of providing an interrupted cutting edge along each tooth. One form of such "chip breaker" is described in the Erhardt U.S. Pat. No. 2,855,657 dated Oct. 14, 1958. These attempted solutions to the aforementioned problems have met with some success in improving tool life and in facilitating chip removal from the work area, although such success is due primarily to the fact that smaller, discontinuous chips are produced which may be more readily removed from the work area. In other words, the solutions have been directed primarily to a form of the chip produced, rather than removal of the chip from the work area.